Preventing Winter Tree Plant Injury
Question: I know there are many types of tree and plant injury out of man’s control. However, what are the best steps, precautions and preventive measures that can be taken to protect the trees and shrubs in our landscape? Renee, St. Louis, Missouri
1. Grow species and varieties of plants which are winter hardy and are adapted to your particular area. Check with your state extension service for recommendations regarding what types of trees and shrubs to plant. Avoid planting susceptible plants except in protected locations and in well-drained soils.
2. Avoid practices which encourage susceptible, tender growth late in the season, such as large summer applications of a high-nitrogen containing fertilizer, heavy pruning and excess watering.
3. Fertilize the soil around injured deciduous trees in the early spring to increase vigor. It is best first to have soil tests made and then follow the recommendations made from these tests. As a general rule a total of two to three pounds of a commercial fertilizer (For example 12-12-12, 10-10-10, 12-6-4, 10-8-6, 10-8-4, 10-6-4, 10-3-3, and 8-5-3) for every inch diameter of the trunk at chest height is sufficient.
Small trees (less than six inches in diameter) should usually receive only half of this amount. Apply the fertilizer in a series of crow or punch bar holes in a circle around the outermost ends of the branches. The holes should be 12 to 24 inches deep and about two feet apart. Feeding needles and compressed-air drills or soil augers are usually used by commercial arborists. Larger trees need several concentric circles of holes, with the outermost circle underneath the branch tips. After putting the fertilizer in the holes, water it in well with a hose for about three days. The holes may be left open or filled with sand, pea gravel, peat moss or rich top soil.
Small evergreens may be injured by commercial fertilizers. Any fertilizer used should probably be a slow-acting, organic type. The fertilizer may be hoed or watered into the soil thoroughly. Broad-leaved evergreens, azaleas, rhododendrons, andromeda, laurel, and the like require an acid soil. For these plants work liberal quantities of acid peat moss or rotted oak-leaf mold into the soil and add more as a mulch. The soils in many areas of mid-America are too basic for these plants to grow unless the soil is artificially acidified.
For shrubby-type pines, spruces and junipers apply about one-half to one pound of commercial fertilizer per plant twice a year, in early spring and again in late spring. Large specimen evergreens usually require two to two and one-half pounds per inch of trunk diameter. The fertilizer is placed in holes 12 to 15 inches deep under the tips of the branches in early spring or in the fall.
Fertilization tends to increase the amount and depth of root growth, hence helping reduce the possibility of severe winter injury.
4. Improve the air and water drainage in heavy, wet soils by shallow spading of the soil under the tree. Susceptible trees always suffer less winter injury where the soil is well-drained.
5. Thoroughly soak the soil out under the branches of trees at two to three-week intervals during dry weather, using long pieces of plastic or “soaker” hose, or a watering lance. Soak the soil thoroughly before freezing weather sets in. Evergreens, especially, should not go into the winter in a dried-out condition.
6. To prevent deep freezing of evergreens, apply an early fall mulch of oak-leaf mold, straw, sawdust or acid peat moss. Mulching also aids in water conservation during dry periods.
7. Protect susceptible evergreens from drying winter winds by planting them in a protected location or, where practical, erect a canvas, burlap or other type of screen.
8. Control destructive insects and diseases.
9. Prune trees and shrubs judiciously to eliminate crowded branches and increase the water supply to the remainder of the plant. Cut out and burn all dead or damaged wood after growth commences in the spring.
10. On sunscald-susceptible (or frost crack-susceptible) trees, paint the trunk with whitewash in the fall; shade the bark with boards, lath, screen, or wrap with burlap, nursery or building paper, cloth, or aluminum foil.
11. Remove dead and decayed bark and wood from sunscald cankers or frost cracks. The surface of the wound should be smoothed, and enough living bark removed from around each wound to give a somewhat egg shape form with the pointed ends running lengthwise of the trunk. Healing proceeds most rapidly if wounds are cut to this general shape. The wound should then be covered with a tree paint to keep out infection and promote rapid healing.
12. Various wax and plastic materials are available in many areas for spraying evergreens. These preparations, when sprayed on valuable shrubs, protect against excessive winter drying. If available, you might try one on a small scale this fall, following the manufacturer’s directions. If good results are obtained, you can spray more plants next year.
by C. Shurtleff
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